Eco‐Friendly SnTe Thermoelectric Materials: Progress and Future Challenges

Abstract

As a key type of emerging thermoelectric material, tin telluride (SnTe) has received extensive attention because of its low toxicity and eco-friendly nature. The recent trend shows that band engineering and nanostructuring can enhance thermoelectric performance of SnTe as intermediate temperature (400-800 K) thermoelectrics, which provides an alternative for toxic PbTe with the same operational temperature. This review highlights the key strategies to enhance the thermoelectric performance of SnTe materials through band engineering, carrier concentration optimization, synergistic engineering, and structure design. A fundamental analysis elucidates the underpinnings for the property improvement. This comprehensive review will boost the relevant research with a view to work on further performance enhancement of SnTe materials.where k B , e, h, m*, µ, and L are the Boltzmann constant, the carrier charge, the Planck's constant, the effective mass of the charge carrier, the carrier mobility, and the Lorenz number, respectively. As can be seen, S, σ, and κ e are interacted and conflict, which raises the difficulty to obtain high ZT. To solve these conflicts, extensive research has been carried out through band engineering to optimize S and σ, [5][6][7] and structuring to reduce the κ l . [8][9][10][11][12] Figure 1a summarizes recent significant achievements in different thermoelectric materials including SnSe, [25] 3%Na-(PbTe) 0.8 (PbS) 0.2 , [70] Cu 2 S 0.5 Te 0.5 , [71] and GeSbTe. [72] As can be seen, the current ZT values of the thermoelectric materials lie between 1 and 2, [7,[13][14][15][16][17][18][19][20][21][22][23] resulting in the fact that the current thermoelectric energy conversion efficiency is comparable to the other energy conversion technologies, such as photovoltaic cells, [22] and solar thermal plants. [22] Considerable research has been continuing to further drive ZT higher than 2 with the predicted efficiency over 20%, [24,25] which can attract highly exciting prospect in the energy generation and conservation fields.In terms of the industrial and automotive applications, waste heats are generally produced in the temperature range of 500-900 K. [26][27][28] To recover such waste heats, developing high-performance mid-temperature (400-900 K) thermoelectric materials is highly desired. For this purpose, lead telluride (PbTe) and its alloys have been considered as a primary material system. [7,10,14,17,29] However, the toxicity associated with Pb causes severe threat to the environment and needs to be alternated for domestic usage. [30] Hence, as its analog, tin telluride (SnTe) [21,[30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] with the rock-salt crystal structure has been inspired with great interests. [32] Especially, SnTe is nontoxic, earth-abundant, and environment friendly, [45] which makes it

Flexible Thermoelectric Materials and Generators: Challenges and Innovations

“…S 2 σ is the power factor and κ is principally constituted by the electronic conductivity (κ e = LσT , where L is the Lorenz number) and the lattice thermal conductivity (κ l ), i.e., κ = κ l + κ e . S can be illustrated by the Pisarenko relationwhere k B , h , and m * are the Boltzmann constant, the Planck constant, and the density of states (DOS) effective mass, respectively . In order to achieve high zT , materials should possess high σ, high S , and low κ.…”

“…[104] S 2 σ is the power factor and κ is principally constituted by the electronic conductivity (κ e = LσT, where L is the Lorenz number) and the lattice thermal conductivity (κ l ), i.e., κ = κ l + κ e . S can be illustrated by the Pisarenko relation [6] π π =      …”

“…Acid-based doping involves the transfer of protons (H + ) or hydrides (H − ) toward the polymer backbone to form a p-or n-type conductive polymer, and corresponding dopants are called acid or base dopants, respectively. [96] Figure 8a illustrates the molecular structures of acid dopants including 4-ethylbenzenesulfonic acid (EBSA), [223][224][225] (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane (FTS), [223] camphorsulfonic acid (CSA), [226] dodecylbenzenesulfonic acid (DBSA), [226] and [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM); [35] and base dopants including leuco crystal violet (LCV), [227][228][229] and benzimidazole derivatives [208,230,231] such as (4- [220] Copyright 2013, RSC Publishing. c) σ and S of electrochemically doped poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) film in the transistor, where in situ characterization was realized.…”

“…Conventional batteries have limited applications in wearable and/or implantable electronics due to their requirements for frequent replacement/recharge and extra‐maintenance; therefore, developing maintenance‐free and energy‐autonomous power sources could have a significant impact on the expansion of the number of applications for the wearable and/or implantable electronics . As an emission‐free power source, thermoelectric (TE) materials and their devices can meet the above requirements by stably and directly converting body heat into electricity through the Seebeck effect, and acting as solid‐state power sources without any vibration . However, conventional bulk TE materials have a number of weaknesses, including being complicated to process and generally heavy and rigid, which limits their applicability, particularly when in contact with curved heat sources, which constrains their commercial applications in wearable electronics.…”

Promising and Eco‐Friendly Cu2X‐Based Thermoelectric Materials: Progress and Applications

“…N v can be increased when multiple bands have similar energy within a few k B T due to either orbital degeneracy (similar extreme energy levels of multi bands) or valley degeneracy (degenerated Brillouin zone of multi carrier pockets due to high symmetry of crystals), while m b * can be increased with flattening band structure . Additionally, resonant levels, which induce a narrow peak in DOS and diffuse conduction electrons in a strongly energy‐dependent manner, are favorable for large S . Reducing κ l through phonon scattering by point defects, strain fields, dense grain boundaries, and interfaces and pores can also increase the zT value.…”